All current telephones are designed for use with modular jacks, so, before extending your phone system, you will have to convert to modular jacks if you don’t already have them.
Hard-wired jacks. Telephone connections installed before 1974 are referred to as “hard-wired” because the telephone could not be unplugged. The so-called “block” attached directly to the wall or trim, and the “flush-mounted” was actually housed in the wall and covered with a faceplate that was round or rectangular.
Both block and flush-mounted connections are easily changed. Simply remove the cover with a screwdriver and replace it with the appropriate modular jack converter.
Four-prong jacks. Portable phones often used a four-prong jack mounted on a wall or trim, or a flush-mounted jack in a housing box covered by a faceplate. You can either replace the four-prong jack with a modular one or use a plug-in adapter that fits the four-prong jack.
Hard-wired phones. Hard-wired desk phones are those with a permanent connection between the line and the phone. To convert these, simply remove the phone housing and install a line cord converter.
Wall phones that are hard-wired cannot be converted. Instead, you must first remove the telephone, which will leave the wires exposed. Do not let them fall back into the wall because you will need them to install a new modular jack.
Once you have your wiring in place, it’s time to install new modular jacks. This quick and simple process requires only a screwdriver.
The three most common types of modular jacks are flush-mounted jacks, wall-phone jacks and surface-mounted jacks.
Refer to the instructions of the one you have chosen to make sure you properly attach each wire to the correct terminal; wires come color-coded to facilitate the installation. Also look for quality jacks with special terminals to accommodate extra wiring, allowing you to route another jack should you need to in the future.
Once you have made the connections, double-check to make sure you have not inserted more than one conductor in a single slot in the terminal.